A long time ago, the universal indicator of a light bulb’s brightness was its Wattage. For example, an 80W light bulb was brighter than a 30W bulb. When using Wattage, it was easy to find light bulbs of equal brightness for replacing old or blown up bulbs. For a long period, this method was fine.
However, when energy-saving lighting emerged and in particular LED lighting, things changed. The energy efficiency of LED light bulbs meant that a higher Wattage did not mean that a bulb was brighter. For example, a 20W LED light bulb would be brighter compared to a conventional 50W light bulb.
The changes brought about by LED light bulbs were not well understood by consumers. It, therefore, became frustrating and confusing to buy light bulb replacements. However, all is not gloom in the lighting industry as there’s an easy way to tell the brightness of one light bulb from another. That way is lumens.
What are lumens?
Well, remember, we mentioned that to measure the brightness of light bulbs, Wattage was used. Well, it turns out Wattage was not the most proper way to tell how bright a light bulb was. This is because Wattage measures the light input of a bulb instead of the output, and the output is what we’re looking for to know how bright a bulb is.
Therefore, the measurement that shows the output of light is lumens. Lumens (lm) are a measure of the amount of light from a light source visible to the human eye. A bulb will appear to be brighter when its lumen rating is higher.
A conventional light bulb from a home might emit between 300-1000 lumens while, emissions from a high-powered floodlight could be in excess of 20,000 lumens. The advantage of using lumens to determine how bright a bulb is, is that lumens work the same way on all types of bulbs.
Therefore, when comparing halogen light bulbs with LED bulbs, the bulb with the higher lumen count will always be the brighter of the two. When purchasing light bulbs, their packaging should state what their lumens count is and the Wattage.
Are Watts still in use?
Although Wattage alone may no longer inform you of the brightness of a light bulb, it’s still a vital measure in other ways. For example, dimmer switches can only handle light bulbs with a specific Wattage, and for safety reasons, the required Wattage shouldn’t be exceeded.
To calculate the efficiency of a light bulb, we need to calculate both the Watts and lumens.
Calculation of lumens per Watt
The energy efficiency of a light bulb isn’t only measured by its brightness. An efficient light bulb has the right brightness and also uses a minimal amount of power. We already highlighted that the higher the lumens, the brighter the light bulbs, and the lower the Wattage, the lesser the power of a light bulb.
Therefore, it goes without saying that a bulb that is high lumens count and low Wattage will be more energy-efficient compared to a bulb whose lumens are low, but Wattage is higher. In simple terms, to know how efficient a light bulb is, we need to know how many lumens it gives out for every Watt.
How many lumens are there per Watt?
To find out how many lumens there are per Watt all you have to do is divide the number of lumens by the number of Watts. For example, if a 10-Watt bulb emits 700 lumens, then the number of lumens per watt(lm/w) is 700/10 = 70 lumens per watt.
Once you understand this formula, it becomes easy to compare the energy efficiency of different bulbs, no matter their types. For example, if a 6W LED bulb emits 400 lumens, its measurement is roughly 67 lumens per Watts. On the other hand, an incandescent light bulb that emits 400 lumens has a Wattage of 40. Its efficiency is 10 lumens per Watts.
With these calculations done, you can now identify the light bulb that is more energy-efficient. Easy, right?
What about light bulbs that look alike?
When looking for the most energy-efficient light bulb, you may find a difference in light bulbs that appear to be more or less the same. One 20W light bulb might be more energy-efficient compared to another 20W bulb.
In such a situation, all you have to do is use the calculations we have highlighted and voila! You’ll identify the brightest and best light bulbs.
How many lumens do I need?
You’re probably wondering the number of lumens you need for lighting your home or even office. Well, there’s no definite answer to this question, nothing like one size fits all. The lack of a specific number is because the number of lumens needed for lighting depends on a number of factors.
Some of these factors include the shape and size of the room you want to light, how high the ceilings are, what’s the color scheme of the room, the type of lamps used and fitting, the areas used to perform tasks that will be illuminated by the bulb, and the needs of the user.
There is, however, a general guide on the lumens needed per square meter (Sq M) for different rooms in a house.
- Kitchen – 300-400 lumens per square meter
- Living room – 400-500 lumens/Sq M
- Hallway – 300 lumens/ Sq M
- Kitchen (task) – 700 – 800lumens/Sq M
- Bedroom – 300 – 400lumens/ Sq M
- Bedroom (to illuminate a task) – 700 -800lumens/ Sq M
- Bathroom – 500 – 600lumens/Sq M
- Bathroom (task illumination) – 500 – 600lumens/ Sq M
- Reading area – 400lumens/ Sq M
How to read light bulb labels
Light bulbs come in labeled packages. The labeling can be quite confusing as it includes Watts, lumens, and Kelvin. These labels are there as compliance of manufacturers with new lighting regulations and technologies.
Before you get frustrated by the information on a light bulb’s packaging, how about we break down what each information means.
Estimated Yearly Cost
The estimated yearly cost is based on a daily usage rate. While your exact usage may differ from what is provided on the packaging, you will have a good baseline on what your approximate rate of use is using the dollar amount noted.
The brightness of light bulbs is measured in lumens. For example, a brightness of 1100 lumens is equal to a 75W bulb.
Life represents the overall expected longevity of the bulb in years. The longevity of a light bulb is based on approximated daily usage.
Energy usage is measured in terms of Watts. With there being a shift to energy-efficient light bulbs, Wattages ranging between 40,60 or 100 are rare to find. Nowadays, the value of the Watts begins from the twenties going all the way down to single digits.
Light appearance is also known as color temperature. The color temperature shows the quality of light, and it ranges from yellow/warm glow to blue/cool light. A standard incandescent bulb features a warmer light that ranges reaches the 2700K. The K stands for Kelvin.
Many fluorescent bulbs contain mercury. The statement that a bulb contains mercury is, therefore, an indication that the bulb comes with instructions on how to dispose of properly when it runs out of life.
Now that you know how lumens interact with Watts and why energy-efficient bulbs have more lumens per Watts, you probably want to know what else to look for in bulbs to choose the energy-efficient ones. Here are other factors to consider when searching for energy-efficient light bulbs.
To identify an energy-efficient bulb, look for the Energy Star label. Looking for the energy label is especially important in LEDs since there’s a difference in the manufacturing quality of different bulbs.
Bulbs of lower quality don’t last as long as higher-quality bulbs. Currently, light experts recommend you get only Led bulbs with the energy label since they’ve undergone numerous quality tests.
With there being continuous technological development in the lighting world, the use of light bulbs that are more energy-sufficient keeps on increasing. Development in lighting technology is how Watts was replaced by lumens.
There is no specific number that identifies what a good lumens-per-Watt range should be. For now, in order for you to identify light bulbs that are energy-efficient, all you have to do is calculate the number of lumens present per Wattage and choose the bulb with a higher lumens count.
It is vital you always keep in mind the golden rule that the higher the lumens count, the more energy-sufficient a light bulb is. You also don’t need to struggle anymore with understanding what the labels on light bulbs packaging mean anymore.
We have identified what each label means, as well as what values are tested by the measurements. It is our belief that the information we have provided about lumens has shown a light on the grey area of lighting.